Field of the Invention
The present invention relates to extraction of threaded bolts and the like having rounded or otherwise damaged heads. Description of the Background Art
Removal of bolts having rounded heads or bolts that are damaged to such an extent that they cannot be removed in the usual manner, typically involves drilling a hole into the bolt and insertion therein a tool called an "easy out" for removal.
One device for removing threaded screws and the like having destroyed or broken-off heads is disclosed in expired U.S. Pat. No. 1,785,847 to Valentine. The Valentine device includes a threaded member axially disposed within a toothed screw-moving member, and requires that the damaged screw be drilled and tapped. The teeth of the screw-moving member have edges which are perpendicular to the axis of the device, and are forced to dig into the material of the damaged screw by rotation of a nut against the axially disposed threaded member screwed into the drilled and tapped hole in the damaged screw.
An obvious drawback of devices which require drilling and tapping of a damaged screw or bolt is the time involved to effect such drilling and tapping. Drilling of the damaged screw or bolt may contaminate a gearcase with metal fillings making complete drainage and cleaning necessary. Lack of electric current for field work further complicates drilling the damaged bolt.
Toothed bolt extracting-type devices which do not require drilling and tapping of a damaged bolt or screw have been proposed. Examples of such devices are shown in expired U.S. Pat. Nos. 906,040; 1,093,252 and 1,179,680. Other toothed devices for turning threaded members are shown in expired U.S. Pat. Nos. 1,041,440 and 2,622,466.
Prior art bolt extractors of the type which do not utilize drilling and tapping of the damaged bolt or screw have not been generally adopted for reasons which may include principal reliance of such devices on a substantial amount of manually applied rotational force.
There remains a need in the art for an easy-to-use bolt extracting tool which does not require drilling and tapping of a damaged bolt.